This week, NASA has discovered great similarities between the Earth and Mars and Pluto. But when it comes to the potential for life, Mars is an increasingly hot favourite.

This digital false-colour image shows the dark, narrow streaks on Martian slopes inferred to be formed by seasonal flow of water on the planet. The streaks are roughly the length of a football field.
Image Credit: NASA/JPL-Caltech/Univ. of ArizonaSeptember 29, 2015